This invention generally relates to electronically controlled motors and to systems, such as refrigeration systems having motors therein for driving compressors.
Refrigeration systems typically include motors for driving compressors or other components which have several shortcomings, including operating at a single speed. Particularly, an original equipment manufacturer cannot easily adapt a conventional motor to a number of different applications. Each system uses a motor designed to operate at a particular speed corresponding to that system rather than providing for selecting among various speeds late in the manufacture process. For this reason, it is difficult to operate a particular motor in connection with a number of refrigeration systems having compartments of various sizes or walls of various thicknesses. Further, motors used in many refrigeration systems are not capable, of driving the system's compressor at its maximum speed when the system requires rapid cool down and/or operating at a speed selected for maximum efficiency at all other times. Therefore, such motors are ill-suited to increasing refrigerating capacity on demand while providing improved thermal compression and heat exchange efficiencies available at low speed operation for the majority of operating time.
Further, variable speed motors, such as many electronically commutated motors, may be too costly for application in typical refrigeration systems. The control circuits for these electronically controlled motors support various applications through the use of external integrated circuits. External IC support, though, increases the parts count as well as the size of the printed circuit board which results in greater cost for the compressor drive system.
Electronically commutated motors are disclosed in U.S. Pat. Nos. 4,642,537 and 4,757,241 and application Ser. No. 07/889,708, filed May 27, 1992, all of which are commonly assigned with the present application and the entire disclosure of which is incorporated herein by reference in its entirety.